Thyroid Cancer

The most common type of thyroid cancer is well-differentiated thyroid cancer, and consists of papillary thyroid carcinoma and follicular thyroid carcinoma. With good treatment, both these cancers usually have an excellent prognosis with good long term survival. Other types of thyroid cancer include medullary and anaplastic thyroid cancer.

Thyroid cancer can occur at any age and affects women more often than men. A lump in the thyroid gland is the most common way thyroid cancer presents. Thyroid cancer can also present with a lump in the side of the neck (from an enlarged lymph node), a hoarse voice, and swallowing or breathing difficulties.

The treatment of most thyroid cancer is:

  1. removal of the thyroid (thyroidectomy),
  2. sometimes removal of lymph nodes in the neck (neck dissection)
  3. and/or radioactive iodine (RAI).

Types of Thyroid Cancer

There are four main types of thyroid cancer.

  1. Papillary thyroid carcinoma is the most common type of thyroid cancer and tends to spread to lymph nodes. With good treatment it has an excellent prognosis. There are several variants of papillary thyroid carcinoma (tall cell variant, columnar cell variant, hob nail variant, diffuse sclerosing variant, solid variant, TERT positive) that have a worse prognosis.
  2. Follicular thyroid carcinoma is the second most common type of thyroid cancer and tends to spread to lungs, brain and bones via the blood stream. It also has an excellent prognosis.
  3. Medullary thyroid carcinoma is less common. It sometimes runs in families and has an intermediate prognosis. A blood test looking for calcitonin is a very useful marker to help diagnose medullary thyroid carcinoma and to assess response to treatment.
  4. Anaplastic thyroid carcinoma is a very aggressive thyroid carcinoma and has a very poor prognosis.

The Treatment of Differentiated Thyroid Cancer

Differentiated thyroid carcinoma (DTC) is the term given to encompass both papillary thyroid carcinoma and follicular thyroid carcinoma. The American Thyroid Association (ATA)1 has guidelines on the treatment of differentiated thyroid carcinoma. In New Zealand we generally follow the ATA guidelines. The ATA guidelines tend to be updated about every 5-10 years.

The treatment of DTC usually involves one or more of the following:

  1. Surgery
  2. Radioactive iodine
  3. Thyroxine

External beam radiotherapy is indicated for some distant metastases and in anaplastic thyroid carcinoma. Targeted agents are used in some patients with distant metastases and in some aggressive types of thyroid cancer.

The 2009 ATA guidelines on the treatment of DTC divided patients with DTC into a three-tiered risk system: low risk, intermediate risk and high risk. In the 2015 guidelines this three-tiered risk system was further described as a continuum of risk. Patients with DTC are discussed at a thyroid multidisciplinary meeting and treatment recommendations are made.

Twenty years ago, nearly all patients with DTC were treated with total thyroidectomy, radioactive iodine (RAI) and a suppressive dose of thyroxine. Nowadays treatment of DTC is more selective and is guided by the level of risk. Many patients are now treated with hemithyroidectomy alone and without either RAI of a suppressive dose of thyroxine.  Of course, patients treated with a hemithyroidectomy avoid the need to take thyroxine and the potential complication of hypocalcaemia.

The extent of surgery is determined by the extent of the disease and the pathology. Patients with multifocal cancer, cancers greater than 4 cm, lymph node involvement, and aggressive thyroid cancers, are all treated with total thyroidectomy.  Patients with DTC and involvement of cervical nodes require a neck dissection in addition to total thyroidectomy.

Patients with cancers less than or equal to 4cm, localised to one thyroid lobe, with no lymph node involvement, and no spread beyond the capsule of the thyroid gland, can be treated with hemithyroidectomy (removal of involved thyroid lobe only). (See thyroidectomy section.)

Patients with DTC treated with total thyroidectomy need thyroid hormone replacement therapy (thyroxine). The dose of thyroxine is monitored with serial TSH and fT4 measurement. The target level of TSH is determined by the risk stratification of the patient and is usually determined by the patient’s endocrinologist.

The target TSH level for the lowest risk patients is between 0.5-2.0mU/L (low end of normal range),  

intermediate risk patient (0.1-0.5mU/L),  

and for the highest risk patients is <0.1mU/L.

A suppressive dose of thyroxine inhibits thyroid cell growth. A suppressive dose of thyroxine is associated with an increased risk of osteoporosis (3.5x), hypertension, cardiac arrhythmias and ischaemic heart disease. (See thyroid medication section).

Radioactive iodine is recommended for patients with differentiated thyroid cancer that falls into the high-risk category, and some patients in the intermediate risk category. (See radioactive iodine section.) 

Patients with DTC are followed clinically and with ultrasound. Patients with DTC treated with total thyroidectomy are also followed with serum thyroglobulin and anti-thyroglobulin antibodies. Thyroglobulin is a marker of thyroid tissue. Both benign, and some malignant thyroid cells, secrete thyroglobulin.

The thyroglobulin level is interpreted in conjunction with the TSH level (stimulated or unstimulated thyroglobulin level). An undetectable stimulated thyroglobulin level combined with a low level of anti-thyroglobulin antibodies is associated with an excellent prognosis. With good treatment patients with DTC usually have an excellent prognosis.

Papillary Thyroid Microcarcinoma

Papillary thyroid microcarcinoma is defined as a papillary thyroid carcinoma measuring 1cm or less. Treatment of this entity is controversial. Many specialists advocate active surveillance with serial ultrasound. Some specialists advocate hemithyroidectomy and others advocate radiofrequency ablation. The ATA guidelines support RFA of microcarcinoma in selected patients1 as an alternative to active surveillance or resection for cT1aN0M0 PTC in selected patients.

Non-invasive follicular Thyroid neoplasm with papillary like nuclear features (NIFTP)

NIFTP is a new name for a very low-risk thyroid tumour previously known as encapsulated non-invasive follicular variant papillary thyroid carcinoma. It is best regarded as benign.

Medullary Thyroid Carcinoma

The American Thyroid Association has separate guidelines for the treatment of medullary thyroid carcinoma.2 Patients with medullary thyroid carcinoma are generally treated with total thyroidectomy and central neck dissection, plus or minus lateral neck dissection. In addition to clinical and radiological follow up, serial calcitonin measurement is an important part of their follow up regime. Usually, medullary carcinoma has a less favourable prognosis than DTC.

Anaplastic Thyroid Carcinoma

Finally, the ATA has separate guidelines for the treatment of anaplastic thyroid carcinoma. It has the least favourable prognosis of the four main types of thyroid carcinoma, with very few people achieving long term survival. Surgery is indicated only if complete resection is possible with minimal morbidity. Debulking procedures are not recommended. Treatment is mainly with chemotherapy and radiotherapy.

See thyroidectomy section of the site.

References
  1. Ringel MD, et al. 2025 American Thyroid Association Management Guidelines for Adult Patients with Differentiated Thyroid Cancer. Thyroid 2025; 35(8): 841-985.
  2. Wells SA, et al. Revised American Thyroid Association Guidelines for the Management of Medullary Thyroid Carcinoma. Thyroid 2015 25(6): 567-610.